518 



ON THE PHYSIOLOGICAL ACTION OF CASCA BARK. 



muscles being very much less under the influence of the vaso- 

 motor centre in the medulla. As casca acts on the vessels 

 without this centre, however, it was natural to suppose that 

 other vessels than those of the intestines might be affected; 

 and this the curves show to be the case. During the stoppage- 

 of the heart (Experiment XLII) for half a minute the pressure 

 fell only slightly. Now Ludwig and Hafiz found that when 

 contraction of the abdominal vessels was produced by irritation 

 of the vasomotor centre in the medulla oblongata, complete 

 stoppage of the heart was followed by a rapid fall in the blood- 

 pressure, the blood finding its way out of the arterial system 

 into the veins through the vessels of the muscles. The slow 

 fall after the administration of casca shows that the vessels of 

 the muscles must be contracted as well as those of the skin and 

 intestines. 



Action on Secretion of Urine. 



A detailed account of our experiment on the action of the 

 drug on the urinary secretion, together with the accompanying 

 effects on the circulatory system, will be found in pp. 503 and 

 504. Underneath is a diagram showing the close dependence of 

 the rate of secretion of urine upon the blood-pressure (Fig. 161) 



Experiment XXXIII.— March 31. 







Is 

 s 



Fia. 161. 



